Optical fibers are widely used for making telecommunication networks and for data transmissions in industrial environments, in aeronautics, and more generally in all applications requiring wide pass bands and insensitivity to electromagnetic radiation or parasites.
Optical fibers are made of special glass, usually doped with lead to improve transparency. The transmitted signal is detected by phototransistors. Electronic components are now the factors that limit the pass band. Their operating frequencies are very much lower than the pass bands of optical fibers. Consequently, electronic components limit the performances of a data transmission process using optical fibers.
To overcome this disadvantage, it has been proposed to make better use of the pass band of optical fibers by multiplexing several signals before transmission.
Wavelength Division Multiplexing (WDM) is a technique used in the prior art to take advantage of the pass band of single mode fibers. A multiplexer is a component that injects two (or more) signals with different wavelengths on the same line. Signals are separated at the other end of the line by a demultiplexer. Since these are reversible components, the same coupler can be used as a multiplexer or demultiplexer, although the isolation performance of the demultiplexer usually has to be better than that of the multiplexer. Typical units are designed for wave lengths of 1300/1550 nm which can double the capacity of existing lines, but the spectral response of a coupler can also be manipulated for other applications, for example, lasers and amplifiers with erbium doped fiber also require multiplexers.
These multiplexers in the prior art are not fully satisfactory, since the number of channels that can be mixed is limited and is fixed once and for all at the time of their manufacture. Furthermore, processes for making this type of multiplexer are expensive and depend on the nature of the light signals to be mixed.
The purpose of this invention is to suggest a process for optimizing the pass band of an optical fiber and reduce the cost of the optical components. Another important purpose of the invention is to add data circuits without the need to replace multiplexing means.